An ion mobility spectrometer has been developed from the 1970 s in order to detect and analyze organic materials or pollutant materials in the air. By using the ion mobility spectrometer, the kind and the amount of a sample gas can be analyzed in a short time based on a peak current measured in the spectrometer and a moving speed of ions arriving at a collector.
The ion mobility spectrometer has been used to detect mines or components of chemical agents for the military purpose. Recently, it has been gradually applied widely in rummage for bearer of drugs or explosive materials, detection for gas leakage from industrial equipment, and the like.
The ion mobility spectrometer is divided into various types according to the structure of an ion reacting region for generating the ions and an ion moving region for making an electric field and causing the ions to move.
As a method of ionizing samples in the ion reacting region, there are the following two methods: a method of generating the ions using corona discharge or ultraviolet rays, and a method of ionizing the sample by using an ionization source such as radioactive isotope. Further, the structure of the ion moving region is generally classified into a conductively inlaid tube (CIT) structure, a stacked ring structure, and an ion lens structure.
FIG. 11 shows a schematic sectional view of a conventional cylinder type ion mobility analyzer, which comprises an analyzer housing 10, an ion moving tube 35 formed with an ion reacting region 15 and an ion moving region 30 installed within the housing 10, a shutter grid 25 installed within the ion moving region 30 of the ion moving tube 35, and an aperture grid 45 and a collector 40 installed within a rear end of the ion moving region 30 of the ion moving tube 35.
Further, a carrier gas source 20 and a sample gas source 30 are disposed at a front end of the housing 10 and a carrier gas and a sample gas supplied through the analyzer housing 10 to the ion reacting region 15, and a drift gas source 71 for supplying drift gas to the ion moving region 30 is connected at a rear end of the housing 10.
The shutter grid 25 is connected to an output terminal of a grid pulse generator 61 and to a timer circuit 60, and prevents the ions generated in the ion reacting region 15 from entering the ion moving region 30 until receipt of a driving pulse from the grid pulse generator. Further, the ion moving tube 35 is electrically connected with a high voltage supply 80 so that a uniform electric field can be generated within the ion moving tube 35.
The carrier gas injected into the ion reacting region 15 reacts with β particles, which are discharged from the ionization source 12 disposed in the ion reacting region 15, to generate positive and negative reactive ions, which react in turn with the sample gas to generate positive or negative product ions.
The reactive ions and the product ions are cut off by the shutter grid 25 while moving into a drift region, and then enter the ion moving region 30 at the moment the shutter grid 25 is opened, and finally move toward the collector 40.
At this time, the inert drift gas injected from the drift gas source 71 moves in a direction opposite to an ion moving direction while colliding with the ions, and is discharged through a drift gas discharge port 36. The ions introduced into the drift region are separated according to weight, size, charge, temperature, humidity, etc. while colliding with the drift gas, and reach the collector 40 at different speeds from one another. Thus, a predetermined current according to the sample gas is generated by the ions detected at the collector.
That is, the components of the sample are analyzed by a spectrum obtained from the current which is outputted from an amplifier 70 after being detected at the collector 40 based on the pulse inputted to the shutter grid 25 and amplified in the amplifier 70, and passing times of various kinds of ions passing through the ion moving region 30, which is measured by the timer circuit 60 connected to the grid pulse generator 61.